1. Field of the Invention
This invention relates to an image processing apparatus and an image processing method for detecting a moving object region in an image photographed by a video photographing unit, such as a camera.
2. Description of the Related Art
Heretofore, in order to monitor or trace an object, such as a person, a vehicle, in a video captured by a video photographing unit, such as an ITV camera, it is necessary to detect the object in the video. For example, when applied to a monitoring apparatus using the ITV camera, it is considered to create a system that photographs a place desired to be monitored, such as a restricted area, by a camera, detects the presence or absence of an object in the video, and alarms when the object enters the monitored place. Further, it can be also applied to the control of a flow of passerby, the market research, etc. by tracing moving persons and surveying the flow of passerby at a place such as a department store, a station, etc. where many persons go in and out.
When an object enters into the video, the brightness of an object region, that is, the luminance value of the object region in the image changes. Therefore, the object can be detected by detecting a region as a differential region in which there is a difference in the luminance value in the image. As a technology for detecting the differential region of image, there is a difference detecting method using a difference between frames and a background difference method using a background image. In the difference between frames, the difference is detected by calculating the difference of the luminance between the image photographed at the present time and the image photographed a unit time before, and it is judged that there is the object in the region having the difference. However, by the difference between two frames of the image photographed at the present time and the image photographed the unit time before, a disturbance, such as the shaking of tree, the waving of water surface or the fluctuation of a flag, etc., is also detected.
On the other hand, in the background difference method, the object region is detected by previously recording an image of the object which is not moved as a background image, and comparing the image photographed at the present time with the background image.
Even in the background difference method, similarly to the difference detecting method using a difference between frames, it is difficult to deal with the shaking of the tree, and the like.
As a technique for removing the object, such as the shaking of the tree, except an object to be detected, for example, there is a technique of analyzing the image in which the object except the object to be detected had appeared in the past and holding it as a plurality of probability distributions. For example, when there is the shaking of the tree, by holding two appearance probabilities of the leaf part and the part at the rear of the leaf as the backgrounds, even if either the leaf part and the part at the rear thereof is appeared, it can be put as the background (for example, refer to a Non-patent Document 1: C.Stuffer, W.E.L. Grimson, “adaptive background mixture models for real-time tracking”).
When the difference values of the image photographed at the present time and the image photographed in the past are binarized by a threshold value processing, a monitoring apparatus which deals with the fluctuation by creating a background image in which the accumulated result of the past difference values is changed to the original threshold value has also been proposed (for example, refer to Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2000-156852).